Exhaust heat at relatively low temperatures of 60 to 70 degrees Celsius such as from engine cooling exhaust heat (hot water in engine jackets) or cooling exhaust heat from industrial processes is present in large quantities throughout the world. However, there are few uses for this type of exhaust heat since the temperature is low, so that this exhaust heat is directly discarded or indirectly discarded via a cooling tower.
An absorption refrigerating machine for producing cold water using exhaust heat water as a heat source is known in the related art. An example for producing cold water at approximately 7 degrees Celsius for air conditioning from cooling water at 30 to 31 degrees Celsius as a cooling source by using a cooling tower is shown by the single effect absorption cycle plotted on the Dühring diagram in FIG. 14.
Refrigerant is evaporated in the evaporator E. The refrigerant shifts along the dashed line between E and A in the figure and is absorbed in the absorber A. The diluted solution whose concentration has dropped is heated in the regenerator G with an external heat source. Refrigerant vapor is discharged in a quantity equal to that of the refrigerant evaporated in the evaporator E, and the diluted solution is concentrated and returned to the absorber A. A heat exchanger X is utilized (for heat exchange between the concentrated solution side X2 and the diluted solution side X1) at this time to recover the heat. The refrigerant vapor generated in the regenerator G shifts along the dashed line between G and C in the figure, is condensed in the condenser C and becomes refrigerant liquid. This refrigerant liquid returns from the condenser C to the evaporator E.
When the evaporation temperature is 5 degrees Celsius, the absorber outlet temperature is 35 degrees Celsius, and the condensation temperature is 35 degrees Celsius, the solution temperature of the regenerator reaches 69 to 74 degrees Celsius. The temperature of the hot water inlet serving as the heat source needs about 75 degrees Celsius.
In other words, in the single effect absorption refrigerating machine, hot water at the temperature of the 65 to 70 degrees Celsius serving as the heat source is too low in the temperature to produce the cold water at approximately 7 degrees Celsius.
There is also a commercial double-concentrating type absorption refrigerating machine capable of producing cold water of less than 10 degrees Celsius for air conditioning applications, using exhaust heat water of around 60 to 65 degrees Celsius as the heat source, and cooling water from a cooling tower of about 30 to 31 degrees Celsius as the cooling source.
In the example shown in FIG. 15, both the regenerators GL, GH have approximately the same heat transfer area, and both the absorbers AL, AH have approximately the same heat transfer area in the double-concentrating absorption cycle plotted on the Dühring diagram. This figure shows an example cycle of this general heat transfer area relationship.
The refrigerant evaporates in the evaporator E, shifts along the dashed line between E and AL in the figure, and is absorbed in the absorber AL.
The diluted solution whose concentration has dropped is heated with an external heat source in the low-pressure regenerator GL. Refrigerant vapor is discharged in a quantity equal to that of the refrigerant evaporated in the evaporator, the diluted solution is concentrated and returned to the absorber AL. At this time, a low-temperature heat exchanger XL (for heat exchange between the concentrated solution side XL2 and the diluted solution side XL1) is utilized for recovering the heat.
The refrigerant vapor generated in the low-pressure regenerator GL shifts along the dashed line between GL-AH in the figure, and is absorbed in the high-pressure absorber AH. The diluted solution whose concentration has dropped in the high-pressure absorber AH is heated with an external heat source in the high-pressure regenerator GH. Refrigerant vapor is discharged in a quantity equal to that of the refrigerant generated in the low-pressure regenerator GL, or in other words the same quantity as that of the refrigerant evaporated by the evaporator E. The diluted solution is then concentrated and returned to the high-pressure absorber AH. A high-temperature heat exchanger XH (for heat exchange between the concentrated solution side XH2 and the diluted solution side XH1) is utilized for recovering the heat from the solution.
The refrigerant vapor generated in the high-pressure regenerator GH shifts along the dashed line between GH and C in the figure, is condensed in the condenser C, and becomes refrigerant liquid. This refrigerant liquid returns from the condenser C to the evaporator E.
The double-concentrating type absorption refrigerating machine therefore contains many internal devices and is large in size. Moreover, the high-pressure regenerators GH and the low-pressure regenerator GL need to generate refrigerant vapor equal in quantity to that of the refrigerant vapor generated by the evaporator E two times. The efficiency is therefore less than half of that of the single effect absorption refrigerating machine. Therefore the double-concentrating type absorption refrigerating machine has been seldom used.
There is also an absorption refrigerating machine capable of operating with exhaust heat water of approximately 65 degrees Celsius as a heat source. However, this refrigerating machine is even larger than the double-concentrating type absorption refrigerating machine, and is expensive, and has low heat efficiency, and therefore is seldom utilized.
There is also an absorption refrigerating machine having a high-pressure and low-pressure absorbers and regenerators (FIG. 16), as is an absorption refrigerating machine intermediate between the single effect and the double-concentrating type absorption refrigerating machines. This type of absorption refrigerating machine is somewhat smaller in size than the double-concentrating type absorption refrigerating machine and has better heat efficiency. Yet an absorption refrigerating machine with better heat efficiency has been demanded.
In FIG. 16, the refrigerant evaporates in the evaporator E, shifts along the dashed line between E and A in the figure, and is absorbed in the absorber A. The diluted solution of the absorber outlet port whose concentration is reduced, is sent to the auxiliary absorber AX, and while being cooled in the auxiliary absorber AX, absorbs the refrigerant vapor (shifting along the dashed line between GX and AX in the figure) from the auxiliary regenerator GX.
The diluted solution, from the auxiliary absorber AX whose concentration is reduced, is sent to the regenerator G, and is heated and concentrated with the external heat source in the regenerator. The refrigerant vapor that was generated, shifts along the dashed line between G and C in the figure, is condensed in the condenser C and becomes refrigerant liquid. This refrigerant liquid returns from the condenser C to the evaporator E. The solution concentrated in regenerator G on the other hand, is further heated and concentrated with the external heat source in the auxiliary regenerator GX, and returns to the absorber A. The refrigerant vapor that was generated, shifts along the dashed line between GX and AX in the figure and is absorbed in the auxiliary absorber AX.
In the solution circulating system in this cycle, a solution pump is required in order to feed the solution from the absorber A to the auxiliary absorber AX having a higher pressure than the absorber. A solution pump is also required for feeding solution from the auxiliary absorber AX to the regenerator G. Balance control of solution flow rate is also required for feeding the total flow rate from the auxiliary absorber AX to the regenerator C, and therefore, the system is complicated.
In other words, when the quantity fed from the auxiliary absorber to the regenerator is too small, solution collects in the auxiliary absorber, and the solution quantity in the regenerator to auxiliary regenerator to absorber system becomes small, and ultimately cavitation occurs due to insufficient quantity of the solution in the solution pump for sending the solution from the absorber to the auxiliary absorber, so that operation is disabled. On the other hand, if the quantity fed from the auxiliary absorber to the regenerator is too large, then the solution quantity of auxiliary absorber is insufficient so that cavitation occurs in the solution pump for sending the solution from the auxiliary absorber to the regenerator and operation is disabled. Therefore, control or the like is required to balance the solution flow rates into and out of the auxiliary absorber.
In view of the above problems with the conventional art, present invention has the object to provide a compact absorption refrigerating machine with improved heat exchanger disposing positioning, better efficiency, and capable of using hot water at 60 to 70 degrees Celsius as a heat source.